Fluid treatment system

ABSTRACT

A water treatment system having a reverse osmosis unit ( 14 ) includes a storage tank ( 40 ) having an outer tank housing ( 42 ) that encloses an expandable bladder ( 50 ). A pressurized region ( 62 ) is defined between the outside of the bladder ( 50 ) and inside of the housing( 42 ). A control valve assembly ( 44 ) controls communication of source water under pressure to pressurizing region ( 62 ) and communicates the region ( 62 ) with a drain ( 22 ). The assembly ( 44 ) includes a pilot valve ( 70 ) that is responsive to a state of dispensing and includes a valve element ( 76 ) that moves between a first dispensing position and a second non-dispensing position. A servo valve ( 72 ) is responsive to position of the pilot valve ( 70 ) and communicates source water under pressure to the region ( 62 ) when the pilot valve ( 70 ) is in the first position thus applying pressure to bladder ( 50 ) to expel treated water and communicates region ( 62 ) to the drain ( 22 ) when dispensing is not occurring so as to allow bladder ( 50 ) to expand as it receives treated water from the reverse osmosis unit ( 14 ).

This application is a 371 of PCT/US00/06848, filed 15 Mar. 2000.

TECHNICAL FIELD

The present invention relates generally to fluid treatment Systems and,in particular, to a storage tank and storage tank control valve for usewith a fluid treatment system, such as a reverse osmosis system.

BACKGROUND ART

It is known to use a storage tank to store a processed fluid produced bya fluid treatment system. For example, reverse osmosis systems are usedto produce potable or drinking water from water sources that containundesirable contaminants, etc. In a typical reverse osmosis system,especially in the type of reverse osmosis system used in homes, the rateat which treated water or “permeate” is produced by the system can bevery low. As a result, a storage tank is used to store permeate, so thatrelatively large quantities can be made available when the consumeropens the tap or faucet. In the past, “precharged” storage tanks areused. In this type of storage tank, a bladder is used to define apressurized chamber, usually filled with a compressible gas, such asnitrogen. The bladder isolates the gas from the processed water receivedby the tank. As processed water or “permeate” (in the case of a reverseosmosis system) is received by the tank, it gradually compresses the gasin the pressurized chamber. As a result, the permeate is stored underpressure, such that when the faucet is opened, the pressure in thestorage tank exerted by the compressed gas, forces permeate out of thetank and to the faucet.

Although these storage tanks are widely used and provide a suitablemeans for storing permeate, they do have a significant drawback. As moreand more permeate is received by the tank, the pressure needed to effectflow of permeate into the tank increases because as the gas chamber iscompressed, forces on the bladder increase. Accordingly, in order tocompletely fill the storage tank, a significant pressure must be appliedto the permeate as the capacity of the tank is reached. This resistanceto flow exerted by the tank in itself decreases production rate of thereverse osmosis system, since the reverse osmosis system relies ondifferential pressures between the source and the output to effect flowacross the membrane. In addition, as permeate is discharged by the tank,its delivery pressure is gradually reduced as the pressurized gaschamber expands. As a result, the delivery pressure varies significantlybetween a full tank and a nearly empty tank.

DISCLOSURE OF INVENTION

The present invention provides a new and improved fluid treatment systemthat includes a storage system for storing processed fluid such aswater. The storage system receives the processed fluid at substantiallyzero pressure and discharges the stored fluid at a pressure that issubstantially the pressure of the source of fluid being treated.

In the preferred and illustrated embodiment, the invention is disclosedin connection with a reverse osmosis unit. It should be understood,however, that the invention has broader applicability and should not belimited to a reverse osmosis application.

In accordance with the invention, a storage system is disclosed forstoring treated or processed water discharged by a water treatment unit.The storage system includes a tank assembly having an outer tank housingthat encloses an expandable bladder. A pressurizing region is definedbetween an outside of the bladder and an inside of the outer tankhousing. A control valve is disclosed that controls the communication ofsource water under pressure with the pressurizing region and alsocontrols the communication of the pressurizing region with a drain, sothat under predetermined operating conditions, source water in thepressurizing region is allowed to flow to a drain in order to allow thebladder to expand as it receives treated water.

In the illustrated embodiment, the control valve includes a fluidpressure operated control device that is responsive to a dispensingdevice through which the treated water is dispensed. In particular, thecontrol device is operative to connect the source water to thepressurizing region when the dispensing device is dispensing treatedwater and is operative to communicate the pressurizing region with thedrain when the dispensing device is not dispensing water.

In the preferred embodiment, the control device includes a pilot valveresponsive to fluid pressure in a supply conduit feeding the dispensingdevice and is movable between at least two positions. A servo valve alsoforms part of the control device and is responsive to the positions ofthe pilot valve.

The pilot valve includes a source water port, a common port and a drainport and further includes a piston operated flow control member forcontrolling the communication between the common port and the sourceport and between the common port and the drain port. Similarly, theservo valve includes a source water port, a common port and a drainport, as well as a piston operated flow control member for controllingthe communication of the common port with either the source water portor the drain port. The ports of the servo valve are sized to permitrelatively unrestricted flow and, hence, the servo valve controls theflow of source water to the pressurizing region of the tank assembly,and the flow of source water from the pressurizing region to the drain.

In a more preferred embodiment, the water treatment unit disclosed is areverse osmosis nodule having a permeate output, a source water inputand a concentrate output. In the illustrated reverse osmosis system aprefilter is positioned upstream of the reverse osmosis module andfitter source water before it enters the reverse osmosis unit and thepressurizing region of the tank. According to a further feature of thisembodiment, a post filter filters permeate before it is delivered to thedispensing device, e.g., a faucet or tap.

According to a preferred embodiment, the control valve assembly forcontrolling the pressurization and depressurization of the pressurizingregion of the tank is mounted directly to the tank. In accordance withthis embodiment, the tank includes an internally threaded neck which isadapted to receive external threads formed on the control valve orhousing. The control valve assembly is threaded into the neck of thetank and is easily removed for service or replacement.

According to another feature of the invention, a lower portion of thecontrol valve assembly includes a depending, threaded segment which, inconjunction with a internally threaded retaining nut serves as asecurement for the elastomeric bladder contained within the tank.According to this preferred embodiment, the retaining nut includes aradial flange which supports a bladder retaining bearing. As theretaining nut is threaded onto the lower segment of the valve, thebearing captures a neck of the bladder between itself and a taperedsegment on the control valve, thus securing the bladder to the controlvalve. The bearing ring facilitates rotation of the retaining nut wheneither installing or removing the bladder.

Additional features of the invention will become apparent and a fullerunderstanding obtained by reading the following detailed descriptionmade in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of a reverse osmosis systemconstructed in accordance with the preferred embodiment of theinvention, shown in a state in which it is delivering treated water orpermeate;

FIG. 2 is another schematic representation of the reverse osmosis systemshown in a state in which it is not delivering permeate;

FIG. 3 is a top plan view of a control valve and associated storage tankassembly constructed in accordance with the preferred embodiment of theinvention;

FIG. 4 is a sectional view of the control valve and storage tankassembly as seen from the plan indicated by the line 4—4 in FIG. 3;

FIG. 5 is an enlarged fragmentary view of a portion of the control valveand tank assembly as indicated by the detail line 5—5 in FIG. 4;

FIG. 6 is a sectional view of the control valve and tank assembly asseen from a plane indicated by the line 6—6 in FIG. 3; and,

FIG. 7 is an enlarged, fragmentary view of a portion of the controlvalve and tank assembly as indicated by the detail line 7—7 in FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2 schematically illustrate a reverse osmosis system forproducing potable water and that embodies the present invention. FIG. 1schematically illustrates the operation of the system when processedwater is not being delivered, i.e., a tap or faucet is closed; whereasFIG. 2 illustrates the operation of the system when processed water isbeing delivered to a tap or faucet.

The system is connected to a source of water to be processed, indicatedgenerally by the reference character 10. In the illustrated embodiment,the processed water is delivered to a faucet indicated generally by thereference character 12. The illustrated system includes a conventionalreverse osmosis (RO) unit 14. Those skilled in the art will recognizethat the RO unit 14 houses a reverse osmosis membrane (not shown) andincludes an inlet port indicated generally by the reference character16, through which the unit 14 receives water to be processed from thesource 10. The unit 14 also includes a permeate outlet port indicatedgenerally by the reference character 18 and a “concentrate” outputindicated generally by the reference character 20 which communicateswith a drain 22. The RO unit 14 may operate in a conventional manner. Asis known, water to be processed is communicated to the inlet port 16 andis delivered to an internal chamber (not shown) containing the reverseosmosis membrane. Relatively pure water termed “permeate” is allowed topass or permeate through the membrane and is discharged from the unit 14by way of the permeate outlet port 18. Contaminants and other materialremain on the input or concentrate side of the membrane and areultimately discharged through the concentrate output 20 and dumped tothe drain 22. A thorough explanation of the operation of an RO unit thatmay be utilized with the present invention can be found in U.S. Pat.Nos. 4,629,568 and 4,650,586, which are owned by the assignee of thepresent application and are hereby incorporated by reference.

The illustrated system also includes a prefilter 30 which filters largeparticle contaminants out of the source water to inhibit plugging of thereverse osmosis unit and a post filter 32 for performing a finalfiltering or “polishing” of the treated water before delivery to thefaucet 12. The post filter 32 may be in the form of a carbon filter tofurther improve the quality and taste of the processed water. Theprefilter 30 and post filter 32 are considered conventional and do notform part of the present invention.

Permeate produced by the RO unit 14 is delivered to the faucet 12 from astorage tank 40 under the control of a control valve assembly indicatedby the phantom line 44. As will be explained, the tank 40 and controlvalve 44 may form a single, integrated assembly.

The tank 40 includes a relatively rigid outer housing 42 and an internalelastomeric bladder 50. The bladder 50 is the component which actuallystores permeate and expands to accommodate permeate delivered to thebladder via passage 52. As permeate is delivered to the bladder 50, thebladder expands until it fully conforms to an inside surface 42 a of thetank at which time the tank is considered full or at capacity.

Permeate in the bladder 50 is delivered to the faucet 12 by pressurizingan outside surface 50 a of the bladder 50 with water at source pressurevia passage or line 54. To facilitate the explanation, the regionbetween the outside surface 50 a of the bladder 50 and the insidesurface 42 a of the tank shell 42 will be referred to as a region 62.The pressurization and depressurization of the region 62 is controlledby the control valve assembly 44.

As seen schematically in FIGS. 1 and 2, the control valve assembly 44includes a pilot valve 70 and a servo valve 72. As will be explained,the pilot valve 70 responds to the opening and closing of the faucet 12.The servo valve 72 controls the pressurization and depressurization ofthe region 62 and, in particular, controls the communication of thesource water to the region 62 and the venting of the region 62 to thedrain 22. The position or state of the servo valve 72 is controlled bythe pilot valve 70.

The pilot valve 70 includes a diaphragm/piston 76 and a isolated pistonchamber 78. When the piston chamber 78 is pressurized the piston 76 isdriven downwardly to the position shown in FIG. 1. As will be explained,the piston chamber is pressurized via a signal passage 80 whichpressurizes when the faucet is closed. Referring also to FIG. 2, thepilot valve 70 includes a source water port 82, a common port 86 and adrain port 90. A spool-like element 94 defining a single land 94 a isconnected to the piston 76 controls the communication between the sourceport 82 and the drain port 90 with the common port 86. The spool member94 reciprocates within a spool chamber 96. As seen in FIG. 1, when thefaucet 12 is closed, the source water port 82 is communicated with thecommon port 86.

The servo valve 72 is similar in operation to the pilot valve 70.However, the servo valve is constructed such that it can sustain muchhigher flow rates through its ports. The servo valve 72 includes adiaphragm supported piston 100 and an isolated, piston actuation chamber102. The servo valve 72 includes a piston chamber port 106 which isconnected via signal line or passage 108 to the common port 86 of thepilot valve 70. When the piston chamber 102 is pressurized, the piston100 is driven upwardly (as viewed in FIG. 1) to the upper position shownin FIG. 1. In the absence of fluid pressure in the piston chamber 102,the piston 100 moves downwardly to the position shown in FIG. 2 at whichpoint it abuts a stop 110.

The servo valve 72 includes a common port 112, a drain port 114 and asource water port 116. The fluid communication between these ports iscontrolled by a spool element 120 having a single land 120 a. The spoolelement is connected to and is preferably integrally formed with thepiston 100. The land 120 a reciprocated within a spool chamber 122. Theports 112, 114 and 116 communicate with the spool chamber 122.

Referring first to FIG. 1, when the servo valve piston 100 (and hencethe land 120 a) is moved to its upper position as viewed in FIG. 1, thecommon port 112 is communicated with the drain port 114 via the spoolchamber 122. In this position, water in the region 62 of the tank 40 isallowed to proceed to the drain 22 via tank line 54, which communicateswith spool chamber 122 via the common port 112. The source water thenflows out of the spool chamber 122 through the drain port 114 and iscommunicated to the drain 22 via a common drain line 130. Thus, as thebladder 50 expands to receive permeate being produced by the RO unit 14during water production, any source water is driven out of region 62 andis discharged to the drain 22. This allows the bladder 50 to expandcompletely to conform to the inside surface 42 a of the tank shell 42.

The piston 100 of the servo valve 72 is driven to the upper position asviewed in FIG. 1 by a signal pressure received from the pilot valve 70.In particular, when the faucet is closed the pilot valve chamber 78 ispressurized driving the piston 76 downwardly to the position shown inFIG. 1. In this position, source water is communicated to the spoolchamber 96 via the source water port 82. The water in the spool chamber96 is delivered to the servo valve piston chamber 102 via the commonport 86 of the pilot valve 70 and the signal line 108. As explainedabove, in this state, source water in the region 62 is vented to thedrain 22 and the permeate in the bladder 50 is at substantially zeropressure. It should be noted that the bladder 50 does exert some minimalpressure on the permeate due to its resistance to expansion.

The inside of the bladder 50 is communicated with the output port 18 ofthe RO unit 14 via the supply line 52. Since the pressure in the bladder50 is substantially zero, the RO unit 14 begins producing permeate anddelivering that permeate to the bladder 50 via the supply line 52. Asthe bladder 50 expands, source water in the region 62 is discharged tothe drain 22 via the circuit explained above.

Referring now to FIG. 2, the operation of the system when permeate isbeing dispensed from the faucet 12 is as follows. When the faucet 12 isopened, pressure in the signal line 80 drops to substantially zero. Theabsence of pressure in the pilot chamber 78 allows the source waterpressure communicated to the spool chamber 96 via source water line 136and source port 82 to drive the piston 76 to its upper position shown inFIG. 2. In this position, the pilot valve common port 86 is communicatedwith the drain port 90. As a consequence, fluid in the servo valvepiston chamber 102 is allowed to proceed to the common drain line 130and, hence, the drain 22 via signal line 108 and the spool chamber 96 ofthe pilot valve 70. As seen in FIG. 2, when the land 94 a is in itsupper position as viewed in FIG. 2, the spool chamber 96 crosscommunicates the common port 86 and the drain port 90.

The communication of the servo valve piston chamber 102 with the drain22 causes the servo valve piston 100 to move downwardly (as viewed inFIG. 2) due to the application of source water pressure to an uppersurface 121 (as viewed in FIG. 2) of the land 120 a of spool 120 via thesource water line 136, branch line 136 a and port 116. When the pistonmoves to its lower position (as viewed in FIG. 2) the source water port116 of the servo valve 72 is communicated with its common port 112. Thisallows source water pressure to flow into the tank region 62 via thesource water line 138. The application of source water pressure to theregion 62 produces a contraction force on the permeate bladder 50driving permeate from the bladder to the open faucet 12 via the permeatesupply line 140 which communicates with the post filter 32. The postfilter 32 in turn communicates with is the faucet 12 via branch line144. It should be noted here that the supply line includes a check valve148 which prevents reverse flow of the permeate in the line into thetank 40 and maintains pressurization of the line 140 when the faucet 12is closed.

It should also be noted here that both the pilot valve 70 and servovalve 72 are operated by differential pressures applied to theirassociated pistons. Turning first to the pilot valve 70, the effectivepressure area of the piston chamber side of the piston/diaphragm isequal to the cross-sectional area of the piston chamber 78. Theeffective pressure area of the underside of the diaphragm/piston (whichis exposed to the fluid pressure in the spool chamber 96) is equal tothe cross-sectional area of the piston chamber 96 minus thecross-sectional area of the control element or spool member 94. Thus, ifsource water pressure is applied to the spool chamber 96 of the pilotvalve 70 via the source port 82 concurrently with the application ofpermeate pressure as exerted by source water pressure in the region 62,a net upwardly directed force is applied to the piston/diaphragm 76 (asviewed in FIG. 2), which causes the piston to move upwardly.

The same relationship exists for the servo valve piston/diaphragm sothat when source water pressure is applied to the servo valve pistonchamber 102, concurrently with source water pressure applied to the endsurface 121 of the control spool/land 120 a via the source water port116 of the servo valve 72, a net upwardly directed force is applied tothe piston/diaphragm 100 causing the piston to move to its upperposition shown in FIG. 1.

With the present system, the overall delivery rate and permeateproduction are substantially improved. During permeate production, i.e.,when the faucet 12 is closed, the permeate reservoir (as provided by thebladder 50) is at substantially zero pressure and, hence, the RO unit 14sees very little resistance to flow thus maximizing flow through the ROunit 14. During delivery of permeate through the faucet 12,substantially full supply pressure is applied to the bladder 50 and,hence, permeate is delivered to the faucet 12 at substantially sourcepressure minus pressure losses due to flow restrictions due to lines andpassages. As a consequence, the flow rate of permeate from the faucet 12is substantially constant since at all times supply pressure is appliedto the exterior surface of the bladder 50 as compared to bladder tanksthat utilize a precharge which results in reduced pressure as permeatein the tank is depleted.

Turning now to FIG. 3-7, a control valve and tank assembly constructedin accordance with the preferred embodiment of the invention isillustrated. For purposes of reference, the apparatus shown in FIGS. 3-7generally corresponds to the items referenced as 44 and 40 in FIGS. 1and 2. To facilitate the explanation, like components in the apparatusshown in FIGS. 3-7 will be given the same reference characters used inFIGS. 1 and 2 followed by an apostrophe.

Accordingly, the control valve/storage tank assembly includes a controlvalve 44′ which is threadedly received by a tank 40′. As previouslydescribed, the tank 40′ includes a relatively rigid tank shell 42′having an inside surface 42 a′. In the illustrated embodiment the tankis made from two tank halves that are joined by a spin welding process.Details of this type of tank construction can be found in U.S. Pat. No.4,579,242 that is owned by the present assignee and is herebyincorporated by reference. The bladder 50′ is disposed within the tankshell 42′ and expands to receive permeate and contract to expelpermeate. The region 62′ located between the outside of a bladder 50′and the inside 42 a′ of the tank 42′ receives source water in order toapply contracting forces on the bladder to expel permeate, whenever thefaucet 12 (shown in FIGS. 1 and 2) is opened.

Referring now to FIG. 5, the components that comprise the control valve44′ (represented schematically in FIGS. 1 and 2) are shown in an actualcontrol valve constuction. The valve housing 44 a which may be inassemblage of individual housing elements, defines a plurality of ports(shown best in FIG. 3). In particular, the housing defines a tank outletport 150, a source water feed port 152, a permeate or product port 154,a drain port 156 and a signal port 158. Referring to FIGS. 1 and 2, inan actual system the above-identified ports would be connected asfollows. The tank port 150 would connect to the conduit 140. The feedport 152 would connect to the conduit 136. The permeate port 154 wouldconnect to the permeate supply port 18 of the RO unit 14 via conduit 52.The signal port 158 would be connected to the conduit 80.

The housing 44 a at least partially defines the pilot valve 70′.Referring, in particular to FIG. 5, the housing 44 a reciprocally mountsthe diaphragm carried pilot piston 76′ in the piston char 78′ at leastpartially defined by the valve 44 a. The piston chamber 78′ communicateswith the signal port 158. As explained above the port 158 is connectedto the signal line 80 (shown in FIGS. 1 and 2) which in turn,communicates with the faucet feed line 144 (shown schematically in FIG.1). In the actual embodiment, flexible conduit is used to connect theport 158 with the faucet supply line and/or the output port of the postfilter 32 using a suitable fitting.

The piston 76′ is connected to a spool 94′ including a land 94 a′; theland 94 a′ sealingly engages the inside of the spool chamber 96′. AnO-ring 159 effects a seal between the land 94 a′ and the spool chamber96′ while permitting reciprocating movement in the land 94 a′. Asdescribed in connection with FIGS. 1 and 2, the land 94 a controls thecommunication of a common port 86′ (shown in phantom) with either thesource water port 82′ or the drain port 90′. In the actual valveconstruction, the ports 82′ and 90′ may be formed by wall openingsdefined in the body of the valve, rather than precisely defined ports.This is the construction shown in FIG. 5.

The servo valve 72′ (the position of which is controlled by the pilotvalve 70) is located immediately adjacent the pilot valve 70′. Itincludes a diaphragm supported piston 100′ that at least partiallydefines a piston chamber 102′. A stop 110′ determines the lowermostposition of the piston 100′. As explained above, the piston is connectedto a spool 120′ which carries a land 120 a′ that is slidably movablewithin a spool chamber 122′. An O-ring 161 is mounted to the land 120 a′land sealingly engages the inside of the spool chamber 122′. The spool120 a′ controls the communication of the common port 112′ with the adrain port 114′ and the source water port 116′. As explained above, theports themselves may be defined by openings formed in the valvebody/housing, rather than precisely defined ports.

As seen in FIG. 5, the piston chamber 102′ is at least partly formed bya bottom cap 160 that is secured to the rest of the valve body by aplurality of threaded fasteners 162 (only one is shown). The interfacebetween the cap and the rest of the valve body is sealed by an O-ring164.

As seen best in FIG. 5, source water from the source water port 152 isdelivered to the spool chamber 122′ by the passage 136′ which isconnected to the spool chamber by a branch passage 136 a′. When theservo piston 100′ is moved to its lowest position as viewed in FIG. 2,source water is communicated from the port 116′ to the common port 112′(via the spool chamber 122′). The common port 112′ delivers the sourcewater to a cavity 170 formed in the control valve that communicates withthe region 62′ via passage 170 a.

When the piston 100′ moves to its upper position, the common port 112′communicates with the drain port 114′ which, as seen in FIG. 5,communicates directly with the drain port 90′ of the pilot valve 70′. Apassage (not shown) communicates these drain ports with the drain 22(see FIG. 1) via the control valve drain port 156 which is connected toan actual drain via a suitable conduit.

When the servo valve piston 100′ is in its upper position (shown in FIG.1), the region 62′ is communicated with the drain 22 (FIG. 1) and,hence, permeate produced by the RO unit 14 (shown in FIG. 1) enters thebladder 50′ gradually expanding the bladder. The actual passage 52 thatis shown schematically in FIG. 1, is suitably molded within the valvehousing.

When permeate is being delivered to the faucet 12 (shown in FIG. 1) theregion 62′ is pressurized upon movement of the servo valve piston 100′to its lower position at which point the common port 112′ communicateswith the source water port 116′. In this position of the piston 100′source water under source pressure to is delivered to the region 62′tending to contract the bladder 50′ thus, driving permeate from thebladder.

As seen best in FIG. 7, permeate is delivered through a passage 180formed in the body of the control valve which communicates with a checkvalve 148′. The check valve 148′ in turn communicates with the dischargeor tank port 150 formed in the valve housing. The discharge/tank port150 is connected to the post filter 32 by a conduit (not shown)represented by the line 52 in FIGS. 1 and 2.

Referring to both FIGS. 4 and 5, the control valve 44′ is threadedlymounted to the top of the tank 40′. In particular, the tank 40′ includesa neck 200 having an internal thread 200 a. A complementary thread 204is formed on the outside of the valve body and is threadedly engageablewith the neck 200 of the tank 40′. An O-ring 208 seals the interfacebetween the tank 40′ and the control valve 44′, but allows the controlvalve 44′ to be removed from the tank 40′ for replacement and/orservice.

As seen best in FIG. 5, the bottom portion of the control valve 44′includes a depending, threaded portion indicated generally by thereference character 220. The threaded portion provides a releasablesecurement for the bladder 50′. In particular, a threaded collar orretaining nut 222, is threadedly received by the lower portion 220 ofthe control valve 44′. The retainer 222 includes an inwardly directedflange portion 222 a, which supports a bladder retaining bearing 226;the bearing 226 facilitates rotation of the retaining nut 222 andsimplifies installation of the bladder 50′. The bladder 50′ includes aneck portion 51 that is captured between the bladder retaining bearing226 and a tapered or cone-shaped segment 228 defined on the lowerportion 220 of the control valve 44′. When the collar 222 is threadedonto the control valve portion 220, the bearing 226 is urged intosealing contact with the neck 51 of the bladder 50′ and secures thebladder to the cone-shaped portion 228 of the control valve 44′.

With the disclosed storage system, permeate is delivered at asubstantially constant pressure to the tap and, as a result, maximumflow rates to the tap are maintained regardless of the amount ofpermeate in the tank. In addition, because the pressurizing region 62 issubstantially zero when permeate is being produced by the reverseosmosis system, the production rate of the RO unit is maximized since itdoes not see increased resistance as the storage tank fills, as is thecase with precharged storage tanks.

Although the invention has been described with a certain degree ofparticularity, it should be understood that various changes can be madeto those skilled in the art without departing from the spirit or scopeof the invention as hereinafter claimed.

We claim:
 1. A reverse osmosis system comprising: a) a reverse osmosisunit having a source water input communicating with a source pressure, apermeate output and a concentrate output; b) a storage tank for storingpermeate discharged by said reverse osmosis unit, comprising: i) a tankhousing; ii) an elastomeric bladder contained with said housing and;iii) structure defining a pressurizing region between an outside of saidbladder and an inside of said tank housing; c) a control valve assembly,comprising: i) a pilot valve responsive to the opening and closing of apermeate dispensing device through which permeate stored in said bladderis dispensed; ii) said pilot valve including a flow control elementmovable between a first and second positions; iii) said control elementmoving to said first position when permeate is not being dispensed bysaid dispensing device and moving to said second position when permeateis being dispensed by said dispensing device; iv) a servo valveresponsive to the positions of said pilot valve control element, suchthat when said pilot valve element is in its first position a flowcontrol member within said servo valve moves to a first position atwhich said pressurizing region in said tank is communicated with adrain; v) said servo valve flow control member moving to said secondposition in response to movement of said pilot valve element, whereinsaid pressurizing region of said tank is communicated with said sourcepressure, whereby contracting forces are applied to said bladder inorder to drive permeate from said bladder of said tank and to saiddispensing device.
 2. A storage device for storing treated waterdischarged by a water treatment unit, comprising: a) a tank assemblyincluding an outer tank housing enclosing within it, an expandablebladder; b) a pressurizing region defined between an outside of saidbladder and an inside of said outer tank housing; c) a valve member forcontrolling the communication of a source water under pressure with saidpressurizing region and for controlling the communication of saidpressurizing region with a drain, said source of water being waterobtained upstream of said water treatment unit; d) a fluid pressureoperated control device responsive, via a signal passage, to adispensing device for said treated water, said control device operativeto connect said source water to said pressurizing region when saiddispensing device is dispensing treated water and operative tocommunicate said pressurizing region with said drain when saiddispensing device is not dispensing water.
 3. The apparatus of claim 2,wherein said control device includes a pilot valve responsive to a fluidpressure at said dispensing device and movable between at least twopositions and said valve member comprises a servo valve responsive tothe position of said pilot valve.
 4. The apparatus of claim 3, whereinsaid pilot valve includes a source water port, a common port, and adrain port.
 5. The apparatus of claim 4, wherein said pilot valvefurther includes a piston operated land for controlling thecommunication between said common port and said source port and betweensaid common port and said drain port.
 6. The apparatus of claim 5,wherein said a servo valve comprises a source water port, a common portand a drain port.
 7. The apparatus of claim 6, wherein said servo valvefurther includes a piston operated spool valve for controlling thecommunication of said common port with said source water port and saiddrain port, said common port and drain port being sized to permitrelatively unrestricted flow of source water out of said pressurizingregion of said tank assembly when said servo valve common port and servovalve drain port are cross communicated by said spool valve.
 8. Theapparatus of claim 7, wherein said water treatment unit comprises areverse osmosis module having a permeate output, a source water inputand a concentrate output.
 9. The apparatus of claim 8, further includinga post filter disposed between a supply conduit communicating with saidtank assembly and said dispensing device whereby treated water dispensedfrom said tank assembly tank is conveyed through said post filter beforebeing dispensed.
 10. A storage system for a reverse osmosis system,comprising: a) a storage tank having a tank housing enclosing anelastomeric, expandable bladder; b) said tank housing and bladderdefining therebetween a pressurizing region for receiving fluid underpressure for exerting contracting forces on said bladder to expelpermeate contained in said bladder; c) a pilot valve responsive, via asignal passage, to the state of a dispensing device such that said pilotvalve moves to a first position when permeate is being dispensed by saiddispensing device and moves to a second position when said dispensingdevice is not dispensing permeate; and, d) a servo valve responsive tosaid pilot valve and operative to communicate source water underpressure to said pressurizing region of said storage tank when saidpilot valve is in its first position and operative to communicate saidpressurizing region with a drain when said pilot valve is in its secondposition.
 11. The apparatus of claim 10, wherein said pilot valve isresponsive to pressure in a permeate supply line feeding said dispensingdevice.
 12. A storage assembly for storing treated water discharged by awater treatment unit, comprising: a) a tank assembly including an outertank housing and enclosing within it an expandable bladder; b) structuredefining a pressurizing region defined between an outside of saidbladder and an inside of said outer housing; c) a control valve mountedto said outer tank housing; d) said control valve including a depending,threaded segment extending into an interior of said tank housing; and,e) a threaded retaining element threadedly receivable by said controlvalve segment and operative to capture a neck portion of said bladderbetween itself and an engagement surface defined by said dependingsegment.
 13. The apparatus of claim 12, further including a retainingelement bearing disposed between said retainer and said bladder neckportion which facilitates relative rotation between said bladder andsaid retaining element.